A typical 8 oz cup of coffee contains about 95–100 mg of caffeine, which takes roughly 10–11 hours to fall below the level that disrupts sleep (~25 mg). Use the calculator above — enter what you drank and when for a precise answer.
Caffeine has a half-life of about 5.5 hours in healthy adults — meaning half of it clears from your bloodstream every 5.5 hours. A 100 mg dose (one coffee) takes about 10–12 hours to drop below the sleep threshold.
At the average 5.5-hour half-life, 100 mg of caffeine (one cup) stays above a sleep-affecting level for about 11 hours. A double espresso (~130 mg) takes about 12–13 hours. Genetics, medications, and pregnancy all affect the rate significantly.
The half-life of caffeine is approximately 5–6 hours for most healthy adults (this tool uses 5.5 hours, per Nehlig et al., 1992). Smokers clear caffeine faster (~3 hr); pregnant women significantly slower (~15 hr).
Coffee itself doesn't have a half-life, but its active ingredient — caffeine — does. The caffeine half-life is about 5.5 hours. After one half-life, 50% of the original dose remains. After three half-lives (~16.5 hr), about 12.5% remains.
Your body clears caffeine exponentially — each half-life, the remaining amount halves. This app computes that curve and tells you when the level drops below 25 mg, the threshold at which adenosine receptor occupancy becomes negligible and sleep is no longer measurably disrupted.
| Substance | Half-life | Source |
|---|---|---|
| Caffeine | 5.5 hr | Nehlig et al., Brain Res Rev 1992 |
| Paraxanthine | 3.5 hr | Arnaud, Food Chem Toxicol 1987 |
Caffeine's half-life of 5.5 hours means a noon coffee still has ~35 mg in your system at midnight. Paraxanthine is caffeine's primary active metabolite — it delivers the same focus and alertness, but clears 36% faster (3.5 hr half-life). The same sleep threshold of 25 mg applies to both, but paraxanthine gets you there hours sooner.
Use the Advanced tab to see exactly how much time you'd save on any given day, then switch if the difference is worth it.
Buy Paraxanthine on Amazon →Landolt et al., Neuropsychopharmacology 1995 · Fredholm et al., Pharmacol Rev 1999
Half-lives vary significantly between individuals based on genetics, liver function, medications, and pregnancy. Values here represent population averages for healthy adults. This tool is for informational purposes only.